Let me try to simplify it for you. "A lot", "many" and "too much" are quantifiers - they are used to descibe the quantity/amount of nouns. Basically, they have similar meanings, but if you put them on a scale of increasing intensity, "many" = "a lot" = a large amount of; "too much" = a large amount of (which is more than enough). The decision on when to use each quantifier depends on the noun- whether the noun is a countable or uncountale noun. For example, you will not say "too many salt", you will say "too much salt" as salt is an uncountable noun. The rule of thumb is that anything that is too small, too numerous or unable to break cleanly into one unit is considered as uncountable. "Very" is an intensifier. It is used as an adverb or adjective (andwhen used infront of a noun as an adjective, it is to emphasize on the noun. eg That very cat you have picked up is sick. ) It is usually used like this- "You are very tall." In this case, it means that the person is more than tall. (like much much taller). Hope this helps! :D

if u'r looking for a detailed explanation , check those out : http://dictionary.cambridge.org/fr/grammaire/grammaire-britannique/much-many-a-lot-of-lots-of-quantifiers https://learnenglish.britishcouncil.org/en/english-grammar/adjectives/intensifiers

There is a lot of difference between them, because they are different parts of speech. I'm very sorry, but there is too much that is different about these words to cover in this little box. If you Google each word, you will find many, many examples of each one.